The Armor of God isn’t physical armor, it’s spiritual. And the most important part of the Armor of God is the Helmet of Salvation. You need to be saved from your sins more than you need anything else in the whole world. You can put on the Helmet of Salvation by believing in Jesus Christ as your Savior.
If a soldier could pick only one piece of armor, they would pick a helmet. It’s so important to protect your head. That’s why you wear a helmet when you ride your bike or go skateboarding or rollerblading. All of the rest of the Armor of God has to do with how you live your life, but the Helmet of Salvation is all about what Christ did for your, not the other way around. If you never put your trust in Jesus Christ to save you from your sins and instead you try to save yourself through your own goodness, then your life’s story will have a very sad ending. You can have all of the other parts of the Armor of God and still lack the most important thing ever. You need the Helmet of Salvation, you need to put your trust in Jesus Christ, you need to be saved.